Reactive composite materials (RCMs) are nanostructured materials comprising two or more solid materials with large negative heats of mixing, such as nickel and aluminum, spaced in a controlled fashion throughout a composite in uniform layers, local layers, islands, or particles. These materials are ignitable to support self-propagating exothermic chemical reactions. The reactions typically travel along the RCMs at speeds ranging from about 0.1 m/s to about 100 m/s.
RCMs may be produced via vapor deposition, mechanical deformation, or electrodeposition. Methods of making and using RCM structures are disclosed in the U.S. Pat. No. 6,736,942 entitled “Freestanding Reactive Multilayer Foils” (“the '942 patent”), which is incorporated herein by reference and in U.S. provisional application 60/692,822 to Xun, et al. filed Jun. 22, 2005, entitled “Methods Of Making Reactive Composite Structures, Resulting Products And Applications Thereof”.
Self-propagating reactions in RCMs are driven by a reduction in chemical bond energy. Upon the application of a suitable stimulus to ignite, a local bond exchange between constituents of the RCM produces heat that is conducted through the RCM to drive the reaction. Recent developments in RCM technology have shown that it is possible to carefully control the ignition threshold and the heat and velocity of the reaction. For instance, it has been demonstrated that the velocities, heats, and/or temperatures of the reactions in an RCM can be controlled by varying the thicknesses or scale of the reactant regions and that the heats of reaction can be controlled by modifying the RCM composition or by low-temperature annealing of the RCM after fabrication.
These technological advances have widened the scope of potential applications of RCMs. Important applications include: (a) reactive multilayer joining (see, for example, U.S. patent application Ser. No. 10/843,352 filed May 12, 2004 which is incorporated herein by reference); (b) hermetic sealing (see, for example, U.S. patent application Ser. No. 10/814,243 filed Apr. 1, 2004, incorporated herein by reference); (c) structural elements that are capable of releasing energy; and (d) initiating secondary reactions, as in flares, detonators and propellant-based devices.
Several different approaches have been employed for igniting self-propagating reactions in RCMs. Such techniques are described in U.S. patent application Ser. No. 10/959,502 (the '502 application) filed Oct. 7, 2004 which is incorporated herein by reference. The stimuli include electric current, mechanical impact, friction, induction heating, microwave radiation, and laser radiation. It is desirable to protect RCMs from unwanted ignition from accidental exposure to such stimuli.